Impact machines are frequently used in quarries, road construction and building construction applications in order to work hard surfaces, such as rock, concrete and pavements or softer materials such as asphalt. The invention can be used on machines such as rock drills, breakers, rammers and hammers which all have a similar impact mechanism.
A common design for impact machines comprises hydraulic, pneumatic, combustion engine or electrical actuating means and a movable impact element transferring an impact force to a work tool attached to the housing. In operation, fatigue in a hard surface may be achieved by applying a continuous impact force from the work tool, such that the hard surface finally breaks. However, parts of the vibrations from the movements of the impact mechanism are transferred to the housing of the impact machine and to a connection point for either a manual handle or to a bracket for a machine attachment. The vibrations may thus result in body injuries if the tool is hand-held and in machine wear if the tool is attached to a machine.
An example of a vibration dampening mechanism for a hand-held machine tool is disclosed in the document US2012/0279741. The vibration damping mechanism comprises a movable counterweight arranged between two identical sets of compression springs. Each set comprises two springs of different lengths arranged in parallel; the longest spring is in constant contact with the counterweight, and the shortest spring is only in contact with the counterweight at high vibration amplitudes.
When the vibration amplitude of the counterweight is increased, the springs that are connected in parallel are both activated, such that the spring constants are added and the spring constant in the vibratory damping mechanism is increased. This shifts the natural frequency of the vibration damping means towards higher frequencies.
The purpose of the short springs arranged at a distance from the counterweight is to prevent striking of the mechanical limit position. Under normal operating conditions, the short springs will not be in contact with the counterweight.
The document DE102009046348 discloses another example of a vibration damping mechanism for a hand-held machine tool that comprises a counter acting weight. In order to provide a cost efficient method of producing the vibration damping mechanism, the geometry of a coil spring can be varied such that a central region of the spring has a certain weight that is sufficient to create a counter-acting weight. The central region is provided with a weight by arranging it like a tension spring with a large diameter and with compact windings. Alternatively, an external or internal counterweight can be attached to the central region to achieve a heavier counterweight. The central region is received between two elastic compression springs that are provided with stiff end-portions connected to a housing. However, the arrangement in DE102009046348 does not provide any means for extending the dampened frequencies range of the machine tool.
In view of the above, it is an object of the present invention to provide an improved vibration damping arrangement for an impact machine that is providing a vibration damping effect throughout a wide working frequency range of the machine and that also reduces the risk of sudden disruptions in the vibration damping effect. A further object is to provide a stronger feed-force of the impact machine, such that the weight of the hammering can be reduced. The inventor was recently given the assignment of trying to find a way to reduce the vibrations of the handles in hand held impact machine. As an example of a machine on the market he was given an impact machine, Atlas-Copco, KV434, having an impact energy of about 25 Joules, and a total weight of 12 kg whereof the impact element had a weight of 0.53 kg. The idea behind the vibration reduction arrangement of this machine, resided in making the machine sufficiently heavy such that the amplitude of the vibrations would be reduced due to the weight of the machine. However, still with this heavy weight, the machine generated very high vibrations in the range around region of 20 m/s2, hand arm weighted acceleration.
In the beginning of the project, the inventor made an analysis of possible ways to lowering the vibrations in the handles, and came up with the following ideas:                (a) providing vibration isolation means (such as springs or shock absorbers) e.g. between the impact mechanism and the handles,        (b) using a actively controlled counterweight, which applies the substantially same force to the housing as the hammering element but in the opposite direction, or        (c) using a tuned vibration absorber.        
Knowing that tuned vibration absorbers, such as the ones described by J. P. Den Hartog in “Mechanical Vibrations”, 1985, or “Shock and Vibration Handbook”, 1987, where a counterweight is coupled to an active weight by means of a spring, would only work within a very limited frequency interval; the inventor quickly gave up that idea. These types of vibration dampers are also referred to as “vibration reduction methods for narrow frequency ranges” in the following text, and are normally applied to devices having a very limited variation in working frequency, such as air plane engines or marine engines.
The reason for the inventor to abandon the idea of using vibration reduction methods for narrow frequency rages, was that the hand-held impact machines of the type the inventor was working with have a working frequency which varies through a wide frequency range, they normally presented a variation of 20-30% in working frequency and sometimes as high as 50%. The working frequency may vary due to e.g. instability in the control of the element e.g. due to instability in the compressed air supply to the machine, due to the operator holding the machine in varying angles in relation to the surface which is to be cut, due to a variation in the force by which the operator presses the machine against the surface, due to a varying surface hardness at different locations in the element which is to be cut, etc (the list is non-exhaustive).
However, as a comparative example the inventor wanted to give an illustration of how badly the “vibration reduction methods for narrow frequency rages” worked for impact machines. But when he was about to connect a counterweight to the housing of the impact machine by means of one spring at each end of the counterweight he realized that he did not have sufficiently strong springs at home to get the right working frequency. Not letting this stop him, he simply used the strongest once he had at hand.
As predicted, the dampening arrangement did not work at all when he turned the machine on. The machine just bounced around, being extremely difficult to control. Try to picture his surprise when, after a while, the bouncing suddenly stopped and there were hardly any vibrations in the handles at all. The inventor turned the machine off and then on again, and still the vibrations were almost eliminated. There was no reasonable explanation to this.
When he later disassembled the machine, he could see nothing unordinary except that the force of the counterweight had compressed the springs, such that there were gaps between the counterweight and the springs. Hence, he could see no other explanation, besides that it was the gap between the spring and the counterweight that had balanced the system. Encouraged by this, he started to simulate the system to see if his conclusions could be correct—and it turned out that they were.
After the inventor had analyzed his findings, he has come to the conclusion that the surprising vibration reducing effect may not only be achieved by arranging a gap between the counterweight and the springs, but also by means of alternative measures as will be described below.
The present invention is described in the independent claim, and advantageous embodiments of the present invention are defined in the dependent claims.
According to a first aspect of the present invention, there is provided an impact machine comprising:    a housing    a hammering element arranged inside said housing, said hammering element is displaceable between a first hammering element position and a second hammering element position,    an impact receiving element attached to said housing (105; 205),    actuating means (115; 215) arranged to cause said hammering element (110; 210) to perform a hammering operation on said impact receiving element (130; 230),    a vibration reduction arrangement (140; 240) attached to said housing (105;205), which comprises:            a counterweight (150; 250) being displaceable in a first axial direction (A) between a first counterweight position (CW1) and a second counterweight position (CW2) in response to the hammering action of said hammering element (110; 210),        at least one motion reversing mechanism (180; 280) each of said motion reversion mechanism comprising at least one spring-action arrangement (160; 260), each of said at least one spring-action arrangements (160; 260), being arranged to reverse the direction of motion of said counterweight (150; 250),wherein        said counterweight (150) is arrangeable at a position located between said first counterweight position (CW1) and said second counterweight position (CW2) from which position said counterweight (150) is movable a first distance (D1) extending in said first axial direction (A) without actuating said at least one spring-action arrangement (160).        
According to a second aspect of the present invention, there is provided an impact machine comprising:    a housing    a hammering element arranged inside said housing, said hammering element is displaceable between a first hammering element position and a second hammering element position,    an impact receiving element attached to said housing (105; 205),    actuating means (115; 215) arranged to cause said hammering element (110; 210) to perform a hammering operation on said impact receiving element (130; 230),    a vibration reduction arrangement (140; 240) attached to said housing (105;205), which comprises:            a counterweight (150; 250) being displaceable in a first axial direction (A) between a first counterweight position (CW1) and a second counterweight position (CW2) in response to the hammering action of said hammering element (110; 210),        at least one motion reversing mechanism (180; 280) each of said motion reversion mechanism comprising at least one spring-action arrangement (160; 260), each of said at least one spring-action arrangements (160; 260), being arranged to reverse the direction of motion of said counterweight (150; 250),wherein            said vibration reduction arrangement (240) further comprises a first end surface (SEnd1), said at least one spring action arrangement (260) being arranged between said counterweight (250) and said first end surface (SEnd1), said at least one spring action arrangement (260) comprising a first spring-action member (261) attached to said counterweight (250), and a second spring-action member (272) arranged in series with said first spring-action member (261) in said first axial direction (A) and being attached to said first end surface (SEnd1) and said first spring action member (261); said first spring-action member (261) having a first spring characteristics comprising a first spring coefficient (k1) within the interval −ktrad≤k1≤ktrad/2 and k1≠0, and the second spring-action member (262) having a second spring characteristics comprising a second spring coefficient (k2) within the interval ktrad/5≤k2≤30*ktrad, and ktrad is determined from the following formula
      F    res    =            1              2        ⁢        π              ⁢                            k          trad                m            
Fres being the resonance frequency of the impact machine at rated power, and m the weight of the counterweight (250).
In more detail, said first spring coefficient (k1) may be arranged within the interval −ktrad≤k1≤ktrad/2, or −ktrad/4≤k1≤ktrad/4, or −ktrad/6≤k1≤ktrad/6. In all embodiments without gap k1≠0, or k1≤0.001*ktrad or k1≤0.01*ktrad; or
k1≥−0.001*ktrad or k1≥−0.01*ktrad. k1<0 may be achieved by means of e.g. pressurized air or magnetic means as described in more details below.
According to a third aspect of the present invention, there is provided an impact machine comprising:    a housing    a hammering element arranged inside said housing, said hammering element is displaceable between a first hammering element position and a second hammering element position,    an impact receiving element attached to said housing,    actuating means arranged to cause said hammering element to perform a hammering operation on said impact receiving element,    a vibration reduction arrangement attached to said housing, which comprises:            at least one counterweight distributed around said hammering element and being displaceable in a first axial direction between a respective first counterweight position and a respective second counterweight position in response to the hammering action of said hammering element, —a respective first motion reversing mechanism for each one of said at least one counterweight, each respective first motion reversion mechanism comprising a first spring-action arrangement being arranged to reverse the direction of motion of a respective one of said at least one counterweight,wherein            each one of said at least one counterweight is arrangeable at a position located between said respective first counterweight position and said respective second counterweight position from which position each one of said at least one counterweight is movable a first distance extending in said first axial direction without actuating said first spring-action arrangement; and wherein    the spring action arrangement of said respective first motion reversing mechanism is arranged inside said respective one of said at least one counterweight,    each of said respective first motion reversing mechanism further comprises a first end surface attached to said housing and arranged adjacent to said respective first counterweight position and    each one of said at least one counterweight comprises a first projecting member, which projecting member comprises an engaging surface, which engaging surface is connected to said respective spring action arrangement and arranged between said respective spring action arrangement and said first end surface in said first axial direction, whereinwhen any of said at least one counter weight is arranged in said respective first counterweight position:    said engagement surface and said first end surface are pressed against each other,    said at least one spring-action arrangement is actuated.
According to a fourth aspect of the present invention, it relates to a impact machine comprising:    a housing,    a hammering element arranged inside the housing, which is displaceable between a first hammering element position and a second hammering element position,    an impact receiving element attached to the housing,    actuating means arranged to cause the hammering element to perform a hammering operation on the impact receiving element,    a vibration reduction arrangement attached to the housing, which comprises:            a counterweight being displaceable between a first counterweight position and a second counterweight position in response to the impact action of the hammering element,        a first motion reversing mechanism located at the first counterweight position, arranged to receive the counterweight when in motion towards the first counterweight position, and arranged to reverse the direction of motion of the counterweight,wherein the first motion reversing mechanism comprises:            a first spring-action member arrangeable at a first distance from the counterweight when the spring-action member is at rest;or            a first spring-action member and a second spring-action member arranged in series such that one of the spring-action members is attached to the counterweight; the first spring-action member having a first spring characteristics and the second spring-action member having a second spring characteristics, which is different from the first spring characteristics.        
The housing may also be referred to as a hammer element housing, which is the housing in which the hammering element is arranged, and also the housing to which the vibration reduction arrangement is attached.
In essence the inventors have realized that the invention relates to an impact machine which is adapted to perform a hammering operation on a surface or an object to be worked upon.
In particular, a vibration reduction arrangement is attached to the housing and comprises a movable counterweight, interacting with a motion reversing arrangement having a non-linear spring characteristics, such that the motion of the counterweight can be brought into a counter-acting movement in relation to the vibrations in the housing of the hammering element thus substantially reducing the vibrations.
Generally for this invention it is desirable to minimize the damping, so that the velocity of counterweight in the opposite direction is as high as possible. If possible even a negative damping is desirable, and this can be achieved e.g. via compressed air. For example the damping at rated power is between −25% and +25% of critical damping. Alternatively the lower end may be −15%, −10%, −5%, −1% or −0.1% or 0% of critical damping. Additionally or alternatively the higher end may be 15%, 10%, 5%, 1% or 0.1% or 0% of critical damping.
In more detail an improved vibration reducing arrangement may be achieved by providing a motion reversing arrangement having a low force zone and a high force zone, wherein the low force zone is activated before the high force zone when the motion of the counterweight is decelerated and reversed. The spring coefficient of the low force zone may correspond to a first spring coefficient (k1) which e.g. is −ktrad≤k1≤ktrad/2, and the spring coefficient of said high force zone e.g. is ktrad/5≤k2≤30*ktra when at least one member of said motion reversing arrangement is prestressed or biased. Alternatively, the spring coefficient of said high force zone is preferably 2*ktrad≤k2≤30*ktrad when said motion reversing arrangement is not prestressed or biased. ktrad is determined from the following formula
      F    res    =            1              2        ⁢        π              ⁢                            k          trad                m            Fres being the resonance frequency of the impact machine at rated power, and m the weight of the counterweight,
Furthermore, two motion reversing arrangement may be provided, one on each side of the counterweight, wherein the sum of the lengths the respective low force zones (length of low force zone 1+of low force zone 2) preferably is at least 30% or at least 40% of the distance between said first counterweight position and said second counterweight position. When k1=0, said low force zone is a gap, when k1≠0 said low force zone may comprise one or more spring action members having a resulting first spring coefficient k1. Moreover, the motion reversing mechanism may be attached to said counterweight and/or an end surface, or being loose (i.e. not attached to anything) as long as the described low and high force zones are provided. As stated above the at least one counterweight can be distributed around said hammering element. According to one example the counterweight is only one counterweight which fully surrounds said hammering element; or alternatively if there are several counterweights, they may be evenly distributed around said hammering element.
The term “without actuating” in: “said at least one counterweight being arrangeable at a position located between said first counterweight position and said second counterweight position from which position said at least one counterweight is movable a first distance extending in said first axial direction without actuating said at least one spring-action arrangement” means that the counterweight can move said first distance without the at least one spring-action arrangement is being compressed. I.e. an influence on the at least one spring-action arrangement by the counterweight moving said first distance does not makes the at least one spring-action arrangement actuated. The engaging surface can also be called connecting surface. More details may be found below.
The counterweight is normally not filled with oil or other liquids for damping purposes. Oil can however be used for lubrication purposes.
According to at least one exemplary embodiment said vibration reduction arrangement further comprises:                a respective second motion reversing mechanism for each one of said at least one counterweight, each respective second motion reversion mechanism comprising a second spring-action arrangement being arranged to reverse the direction of motion of a respective one of said at least one counterweight, and            the spring action arrangement of said respective second motion reversing mechanism is arranged inside said respective one of said at least one counterweight,    each of said respective second motion reversing mechanism further comprises a second end surface attached to said housing and arranged adjacent to said respective second counterweight position and    each one of said at least one counterweight comprises a second projecting member, which projecting member comprises an engaging surface, which engaging surface is connected to said respective second spring action arrangement and arranged between said respective spring action arrangement and said second end surface in said first axial direction (A) whereinwhen any of said at least one counter weight is arranged in said respective second counterweight position:    said engagement surface of said second projecting member and said second end surface are pressed against each other,    said engagement surface of said second projecting member is displaced relative a center of gravity of said counterweight compared to when said counterweight is arranged in a position where said engagement surface of said second projecting member and said second end surface are separated from each other, and    said second spring-action arrangement is actuated.Below is listed a number of exemplary embodiments, which are based a respective one of the four aspects described above.
According to at least one exemplary embodiment said spring action arrangement of said first motion reversing mechanism is separated from said spring action arrangement of said second motion reversing mechanism.
According to at least one exemplary embodiment the first motion reversing mechanism may comprise a non-linear spring with a weaker section and a stiffer section, wherein the weaker section is in contact with the counterweight. Examples of non-linear springs may comprise coil springs with a diameter that changes as a function of the length of the non-linear spring, which may e.g. result in a conical spring shape.
According to at least one exemplary embodiment said spring action arrangement of said first motion reversing mechanism and said spring action arrangement of said second motion reversing mechanism is one and the same.
According to at least one exemplary embodiment said spring action arrangement of said first motion reversing mechanism comprises a first spring action member.
According to at least one exemplary embodiment said spring action arrangement of said second motion reversing mechanism comprises a second spring action member.
According to at least one exemplary embodiment said spring action member of said first motion reversing mechanism is separated from said spring action member of said second motion reversing mechanism.
According to at least one exemplary embodiment said spring action member of said first motion reversing mechanism and said spring action member of said second motion reversing mechanism is one and the same.
According to at least one exemplary embodiment said first spring action member is prestressed, and has a first spring characteristics (k1) within the interval ktrad/5≤k1≤30*ktrad. Alternatively said first spring action member is not prestressed, and has a first spring characteristics (k1) within the interval 2*ktrad≤k1≤30*ktrad.
According to at least one exemplary embodiment said second spring action member is prestressed, and has a first spring characteristics (k1) selected such that the resulting spring characteristics of the two spring actions members is within the interval ktrad/5≤k1≤30*ktrad, when one or both are prestressed. Alternatively, neither of the spring actions members are prestressed and the resulting spring characteristics of the two spring actions members is within the interval 2*ktrad≤k1≤30*ktrad.
According to at least one exemplary embodiment said motion reversion mechanism comprises four spring-action arrangements distributed around said hammering element.
According to at least one exemplary embodiment said counterweight comprises two spring-action arrangements inside said counterweight.
According to at least one exemplary embodiment said two spring-action arrangements are identical.
According to at least one exemplary embodiment said counterweight further comprising restricting means adapted to restrict the movement of said projecting member in the first axial direction and/or in a direction opposite thereto.
According to at least one exemplary embodiment said restricting means comprises at least one first retaining surface attached to said counterweight, and said projecting member further comprises at least one flange, wherein said retaining surface restricts the motion of said flange in the first axial direction and/or in a direction opposite thereto.
According to at least one exemplary embodiment said restricting means further comprises a second retaining surface adapted to restrict the movement of said second projecting member in said second axial direction and/or in a direction opposite thereto, and said spring action member is biased by said first retaining surface and said second retaining surface.
According to at least one exemplary embodiment said vibration reduction arrangement is arranged around said housing, such that said at least one counterweight is rotatable about a central longitudinal axis of said housing, coaxial with said first axial direction.
According to at least one exemplary embodiment said impact machine further comprises counterweight guiding means arranged to cause said counterweight to move in a linear direction between said first counterweight position and said second counterweight position.
According to at least one exemplary embodiment when said at least one counterweight is only one counterweight, said counterweight fully surrounds said hammering element.
According to at least one exemplary embodiment when said at least one counterweight comprises of two or more counterweights, said counterweights are evenly distributed around said hammering element.
According to at least one exemplary embodiment said counterweight comprises an outer truncated elliptical cross-section which is perpendicular to said first axial direction.
According to at least one exemplary embodiment said at least one spring-action arrangement further comprises a first spring-action member and a second spring-action member arranged in parallel in said first axial direction. What is stated herein about the spring coefficient in a system having non-parallel spring members, may also be applied to the resulting spring coefficient of a system having two or more parallel spring action members.
According to at least one exemplary embodiment the first distance (D1) is at least 20%, or at least 40%, or at least 60% or at least 70% or at least 80% of the distance between the first and the second counterweight positions. According to at least one exemplary embodiment a first spring action member and a second spring action member arranged in parallel, wherein said first spring coefficient of said first spring-action member is lower than said second spring coefficient of said second spring-action member, and wherein said first spring coefficient applies to a distance corresponding to at least 10% or at least 15% or at least 20% or at least 25% of a distance between said first and said second counterweight position; and said second spring coefficient applies to a remaining distance between said first and said second counterweight position.
According to at least one exemplary embodiment said impact machine further comprises hammer element guiding means arranged to cause said hammering element to move in a linear direction between said first hammering element position and said second hammering element position.
According to at least one exemplary embodiment said impact receiving element is a work tool.
According to at least one exemplary embodiment said impact machine is handheld.
According to at least one exemplary embodiment said impact machine is arranged to be attached to a machine, preferably a construction machine such as an excavator, backhoe loader or skid steer loader.
According to at least one exemplary embodiment the weight of the hammering element H corresponds to between 20% and 300% of the weight m of the counterweight.
According to at least one exemplary embodiment an impact machine comprises:    a housing,    a hammering element arranged inside said housing, said hammering element is displaceable between a first hammering element position and a second hammering element position,    an impact receiving element attached to said housing,    actuating means arranged to cause said hammering element to perform a hammering operation on said impact receiving element,    a vibration reduction arrangement attached to said housing, which comprises:            a counterweight distributed around said hammering element and being displaceable in a first axial direction between a first counterweight position and a second counterweight position in response to the hammering action of said hammering element, —a first motion reversing mechanism comprising a first spring-action arrangement being arranged to reverse the direction of motion of said counterweight,wherein            said counterweight is arrangeable at a position located between said first counterweight position and said second counterweight position from which position said counterweight is movable a first distance extending in said first axial direction (A) without actuating said spring-action; and wherein    the spring action arrangement of said motion reversing mechanism is arranged inside said counterweight,    said first motion reversing mechanism further comprises a first end surface attached to said housing and arranged adjacent to said first counterweight position and    said counterweight comprises a first projecting member, which projecting member comprises an engaging surface, which engaging surface is connected to said spring action and arranged between said spring action arrangement and said first end surface in said first axial direction whereinwhen said counter weight is arranged in said first counterweight position:    said engagement surface and said first end surface are pressed against each other, and    said at least one spring-action arrangement is actuated.
According to at least one exemplary embodiment an impact machine comprises:    a housing    a hammering element arranged inside said housing, said hammering element is displaceable between a first hammering element position and a second hammering element position,    an impact receiving element attached to said housing,    actuating means arranged to cause said hammering element to perform a hammering operation on said impact receiving element,    a vibration reduction arrangement attached to said housing, which comprises:            a first number of counterweights arranged evenly distributed around said hammering element, each counterweight being displaceable in a first axial direction between a respective first counterweight position and a respective second counterweight position in response to the hammering action of said hammering element, —a first number of motion reversing mechanisms, each comprising a first spring-action arrangement being arranged to reverse the direction of motion of a respective one of said first number of counterweights,wherein            said each one of said first number of counterweights is arrangeable at a position located between said respective first counterweight position and said respective second counterweight position from which position each one of said at least one counterweight is movable a first distance extending in said first axial direction without actuating said at least one spring-action arrangement; and wherein    said first spring action arrangement of each first motion reversing mechanism is arranged inside said respective one of said first number of counterweights,    each of said respective first motion reversing mechanism further comprises a respective first end surface attached to said housing and arranged adjacent to said respective first counterweight position and    each one of said at least first number of counterweights comprises a first projecting member, which projecting member comprises an engaging surface, which engaging surface is connected to said respective spring action arrangement and arranged between said respective spring action arrangement and said first end surface in said first axial, whereinwhen any one of said first number of counter weights is arranged in said respective first counterweight position:    said engagement surface of said counterweight and said respective first end surface are pressed against each other,    said engagement surface is displaced relative a center of gravity of said counterweight compared to when said counterweight is arranged in a position where said engagement surface and said first end surface are separated from each other, and    said at least one spring-action arrangement is actuated.
The present invention provides the advantage of enabling a substantial decrease in the weight of an impact machine, lower vibration amplitude and an extended frequency range of low vibration amplitude. The force from the counterweight on the housing also creates a feed force that improves the efficiency of the machine.
The counterweight moves in a counter-phased movement in relation to the direction of a hammering element, where the travel distance of the counterweight is restricted to a maximum counterweight displacement distance between the first counterweight position and the second counterweight position measured when the machine is operated at rated power. A movement beyond these points is thus not possible, or normally not possible, when the machine is operated at rated power. Hence, depending on e.g. the impact forces, the travel distance of the counterweight may be equal to the maximum counterweight displacement distance, or shorter.
According to said third aspect of the invention the counterweight comprises a projecting member, i.e. a member which, when said counterweight is arranged in said first or second counter weight position, is displaced relative a center of gravity of said counterweight, compared to when said counterweight is arranged in a position where said engagement surface and said first end surface are separated from each other. In other words, when said spring action member is actuated, the projecting member is displaced relative a center of gravity of said counterweight, compared to when said spring action member is unactuated. In these cases, the motion of the center of gravity could preferably be considered when determining the maximum center of gravity displacement distance. I.e. the maximum center of gravity displacement distance equals the distance that the center of gravity of the counterweight travels or passes between the two end positions of the counter weight, when the machine is operated at rated power. In analogy, the center of gravity can also be considered when determining the first center of gravity position. In other words, said first center of gravity position corresponds to that position of the counter weight where the center of gravity of said counterweight is arranged furthest along a first counterweight displacement direction; and said second center of gravity position corresponds to that position where the center of gravity of said counterweight is arranged furthest along a direction opposite to said first counterweight displacement direction, wherein said counterweight displacement direction is equal to said first axial direction (A) or a direction opposite thereto.
The motion reversing mechanisms may be limited in their axial movement by end surfaces, which define fixed surfaces inside the vibration reduction arrangement. Furthermore, they may serve as abutment surface or attachment surfaces for the motion reversing mechanisms. The vibration reduction arrangement may comprise an end surface on each side of the counterweight.
In relation to this invention, the term first spring-action arrangement includes all spring-action members that take part in the reversing of the direction of motion of said counterweight, and which spring-action members are arranged, between a contact surface of the counterweight and a first end-surface.
Further, in relation to this invention, the term second spring-action arrangement includes all spring-action members that take part in the reversing of the direction of motion of the counterweight, and which are arranged between said counterweight and said second end surface.
In relation to this invention, the term discontinuous spring-action force implies a discontinuous change in the force acting upon the counterweight over the maximum counterweight displacement distance, between the first counterweight position and the second counterweight position. Alternatively, a discontinuous spring-action force may be provided by a combination of spring-action members, with different spring coefficients, e.g. first connected to each other in series and then in connection with the counterweight. The spring-action member applies a force on a contact surface of the counterweight. Alternatively, a discrete combination of a spring-action member arranged at a first distance from (i.e. not physically attached to) the counterweight may provide for the discontinuous spring-action force. In the latter example, there is no applied spring-action force on the counterweight throughout the first distance.
When e.g. one non-linear spring abut the counterweight on each end this may be referred to a non-linear spring-action. A non-linear spring may also be referred to as an unlinear spring.
In relation to the present invention, the length of the intermediate distance is determined when the impact machine, as well as the motion reversing mechanism(s), as well as the spring-action member(s) are at rest, i.e. the spring-action member(s) is/are neither compressed nor extended, i.e. the spring-action members are unactuated. In the case of a biased or prestressed spring-action member, the definition of unactuated implies that the spring-action member is only being subject to the inherent biasing force.
Normally, the intermediate distance is most easily determined when the vibration reduction arrangement is positioned with the counterweight's travel direction coinciding with the horizontal plane. Moreover, provided that the spring-action members acting upon the counterweight are at rest, the first distance which hereinafter is also referred to as the gap or the intermediate distance, is defined as a distance between the first and the second end-surface, through which distance the counterweight is freely movable without actuating the spring-action members. In other words, the counterweight is freely movable and the spring-action members are left unactuated. In yet other words, the counterweight is freely movable while all the spring-action members are at rest or unactuated.
A way of determining the length of the gap in the vibration reduction arrangement is to, in the axial direction between the first and the second counterweight positions, measuring:
the distance between the first and second end surfaces,
the unactuated axial lengths of the spring-action members, and
the axial length of the counterweight.
The length of the gap is calculated as the difference between the distance between the first and second end surfaces, subtracted by the length of the counterweight and the axial lengths of the unactuated spring-action members. When there are spring-action members arranged in parallel, the unactuated length is defined by the distal ends of the longest spring-action member. When there are spring-action members arranged in series, the unactuated length is defined by the total axial length of the members in series. Moreover, the axial length of the counterweight is defined by the counterweight contact surfaces which are adapted to be in contact with the contact surfaces of the spring-action members.
When the counterweight comprises at least one projecting member, the distance of the gap D1 is calculated as the distance between the first and the second counterweight position subtracted by the exterior length (maximum axial length) of the counterweight 750 including the extension of the projecting members from the outer surfaces of the counterweight to the respective engaging surfaces.
The term first axial direction is the axial travel direction of the counterweight. The direction is parallel with the axial extensions of the spring action members.
In relation to this invention the term engaging surface, also called contacting surface, of a projecting member refers to the surface of the projecting member, which is in contact with a first or a second end surface when the spring-action member is being compressed. In a similar way, the term contact surface of a counterweight refers to the surface of the counterweight, which is in contact with the spring-action member as the latter is being compressed; this term is normally used when the spring action members are arranged outside the counter weight.
The purpose of the spring-action member is to reverse the motion of the counterweight. Within the scope of the present invention, there are numerous ways of selecting and designing a spring-action member, whereby the invention should not be limited to any particular type. However, depending on the type of spring-action member, different parameters/coefficients may be used to specify the motion reversing capabilities of the spring-action member. In particular, the expression spring characteristics should be interpreted in a wide sense. Some embodiments of the spring-action member present a linear elasticity and may therefore be characterized in terms of a linear spring coefficient k according to Hook's law. Other embodiments of the spring-action member may include materials which present a spring characteristics corresponding to a non-linear spring coefficient. Still other embodiments of the spring-action member may include materials which present a spring characteristics corresponding to a combination of a spring coefficient k and a dampening coefficient c, such as rubber, solid or foamed polyurethane, etc. (The list in non-exhaustive)
Hence, spring-action members may include materials which present a non-linear elasticity, like for instance rubber, steel material, non-linear springs or air cushions. Further, a spring-action member hereby refers to any type of member, which is capable of providing a motion reversing action on the counterweight. In addition, the spring-action member may have various geometric shapes, like a coil spring, rubber ball or a surface, such as a plate.
The advantages include that the vibrations from the impact machine are dampened for a large working frequency range and the absence of a sudden vibration increase enables the vibration reduction arrangement to exclude a safety zone; as well as that many different elements may be applied, giving rise to a vast design freedom.
According to one embodiment, wherein said counterweight is arrangeable at a position located between said first counterweight position and said second counterweight position from which position said counterweight is movable a first distance extending in said first axial direction without actuating said at least one spring-action arrangement, and said at least one spring action arrangement is arranged inside said counterweight, and said vibration reduction arrangement further comprises:    a first end surface arranged adjacent to said first counterweight position and    a second end surface arranged adjacent to said second counterweight position; said first end surface is arranged to receive said at least one spring action arrangement when in motion towards said first counterweight position; and said second end surface is arranged to receive said at least one spring action arrangement when in motion towards said second counterweight position. Said at least one spring action arrangement may comprise one or more first spring action members which are prestressed and having a resulting spring coefficient within the interval ktrad/5≤k1≤30*ktrad. In case the spring action member(s) of the spring action arrangement are not prestressed, they may have a resulting spring coefficient within the interval 2*ktrad≤k1≤30*ktrad.
According to one embodiment there is one motion reversing mechanism on each side of the counterweight. According to one example, said counterweight is arrangeable at a position located between said first counterweight position and said second counterweight position from which position said counterweight is movable a first distance extending in said first axial direction without actuating said at least one spring-action arrangement, and wherein said vibration reduction arrangement further comprises:    a first end surface arranged adjacent to said first counterweight position, and    a second end surface arranged adjacent to said second counterweight position; andsaid at least one motion reversing mechanism comprises a first motion reversing mechanism and a second motion reversing mechanism, and the at least one spring action arrangement of said first motion reversing mechanism is arranged between said counterweight and said first end surface,and the at least one spring action arrangement of said second motion reversing mechanism is arranged between said counterweight and said second end surface.
According to one example, said first spring action arrangement is attached to said first end surface, and said first spring action arrangement is arranged to receive said counterweight when in motion towards said first counterweight position.
According to one example, said second spring action arrangement is attached to said second end surface, and said first spring action arrangement is arranged to receive said counterweight when in motion towards said first counterweight position.
According to one example, said first spring action arrangement is attached to said counterweight, and said first end surface is arranged to receive said first spring arrangement when said counterweight is in motion towards said first counterweight position.
According to one example, said second spring action arrangement is attached to said counterweight, and said second end surface is arranged to receive said second spring arrangement when said counterweight is in motion towards said first counterweight position.
According to one example, said first spring action arrangement is arrangeable at a position located between counterweight and said first end surface from which position said first spring arrangement is movable a first distance extending in said first axial direction without actuating said first spring-action arrangement.
According to one example, said second spring action arrangement is arrangeable at a position located between counterweight and said second end surface from which position said second spring arrangement is movable a first distance extending in said first axial direction without actuating said second spring-action arrangement.
According to one example, wherein said first spring action arrangement comprises a first spring action member, which first spring action member is biased, and/or wherein said second spring action arrangement comprises a second spring action member, which second spring action member is biased.
According to one example, wherein said first spring-action arrangement have spring action members arranged in series or in parallel in said first axial direction; a first spring-action member having a first spring coefficient within the interval −ktrad≤k1≤ktrad/2 and k1≠0, the second spring-action member having a second spring coefficient within the interval 2*ktrad≤k2≤30*ktrad, the second spring member is not prestressed. The first and/or the second spring action member may also comprise a set of spring actions members, said set of spring action members having a resulting spring coefficient according to the above k1 or k2, respectively; and none of the second spring action members are prestressed.
Alternatively, said first spring-action arrangement have spring action members arranged in series or in parallel in said first axial direction; a first spring-action member have a first spring coefficient within the interval −ktrad≤k1≤ktrad/2 and k1≠0, the second spring-action member have a second spring coefficient within the interval ktrad/5≤k2≤30*ktrad, the second spring member is prestressed. The first and/or the second spring action member may also comprise a set of spring actions members, said set of spring action members having a resulting spring coefficient according to the above k1 or k2, respectively; and at least one spring action member, belonging to said set of spring action members having a resulting spring coefficient k2, is prestressed.
According to an exemplary embodiment, the machine further comprising a second motion reversing mechanism located at the second counterweight position, and arranged to receive the moving counterweight as well as reversing the direction of motion of the counterweight,                wherein the second motion reversing mechanism comprises        a first spring-action member;        or        a first spring-action member and a second spring-action member arranged in series such that one of the spring-action members is attached to the counterweight; the first spring-action member having a first spring coefficient and the second spring-action member having a second spring coefficient, which is different from the first spring coefficient.        
Alternatively, the second motion reversing mechanism may comprise a non-linear spring with a weaker section and a stiffer section, wherein the weaker section is in contact with the counterweight. Examples of non-linear springs may comprise coil springs with a diameter that changes as a function of the length of the non-linear spring, which may e.g. result in a conical spring shape.
According to an exemplary embodiment, the gap or the first distance is at least 20%, or at least 40%, or at least 60% or at least 70% or at least 80% or at least 90% of the maximum counterweight displacement distance. Additionally, or alternatively, the gap is at the most 90% or at the most 95% at the most 97% at the most 99% of maximum counterweight displacement distance. In other words, the gap introduces a distance where the counterweight is not subjected to any spring-action force. For example, the system may be designed with spring-action members, such as air cushions.
According to an exemplary embodiment, which features at least two spring-action members connected in series, wherein the first spring-action member being arranged closest to the counterweight, the first spring coefficient is lower than the second spring coefficient, and wherein the first spring coefficient applies to a distance corresponding to at least 10% or at least 15% or at least 20% or at least 25% of the maximum counterweight displacement distance and the second spring coefficient applies to the remaining distance within the maximum counterweight displacement distance. Furthermore, the unactuated length of the first action member may correspond to at least 20%, or at least 40%, or at least 60% or at least 70% or at least 80% or at least 90% of the maximum counterweight displacement distance.
According to an exemplary embodiment, the first spring coefficient is at least 50%, or at least 60% or at least 70% lower than the second spring coefficient.
According to an exemplary embodiment, the impact machine further comprises hammer element guiding means arranged to cause the hammering element to move in a linear direction between the first hammering element position and the second hammering element position, wherein the guiding means comprises an elongated cavity wherein said hammering element is arranged.
According to an exemplary embodiment, the impact machine further comprises counterweight guiding means arranged to cause the counterweight to move in a linear direction between the first counterweight position and the second counterweight position. With guiding means, the movements of the counterweight are controlled so that the travel path is always the same.
According to an exemplary embodiment, the impact receiving element is a work tool, such as a chisel, drill bit or like.
According to an exemplary embodiment, the impact machine is handheld. An efficient vibration reduction arrangement according to the invention is particularly useful for preventing a vibration transfer to a person holding the impact machine. Another advantage is that the vibrations normally only increase gradually as the working frequency of the machine tool shifts out from the damping range, which enables a user to feel and anticipate the rise in vibration, such that body injuries may be prevented. Moreover, with the vibration reduction arrangement according to this invention, it is possible to design the impact machine such that it always stays in a working frequency arrangement with low vibration amplitude of housing between 0.4 and 1 mm peak.
According to an exemplary embodiment, the impact machine is not handheld, but attached to a machine. Examples of such machines may be construction machinery, such as excavators, backhoe loaders or like. Advantages include that less vibrations are transferred to the machine and to the operator, which significantly improves the operating comfort for and reduces the mechanical wear on the machine.
According to an exemplary embodiment, the weight of the impact element corresponds to 20% to 300% of a weight of the counterweight. The purpose of the counterweight arrangement is to counteract the vibrations from the impact element. Depending on the weight and stroke length of the impact element, the counterweight and the travel path between the first counterweight position and the second counterweight position may be adjusted such that the resulting force on the counterweight is equal to the force of the hammering element. Consequently, a counterweight with a weight of less than 100% of the hammering element's weight gives the advantage of a possible reduction in the overall weight in the impact machine. On the contrary, a counterweight with a weight of more than 100% of the hammering element's weight gives a better flexibility to mount the vibration reduction arrangement in view of the geometric constraints of the impact machine, such as the length of the impact machine's housing.
According to an exemplary embodiment, the counterweight comprises one or more elements, evenly distributed with respect to the housing of the hammering element. By distributing the counterweight around the center movement axis of the hammering element, a higher stability is achieved to the impact machine, which also more efficiently absorbs the vibrations distributed in its housing.
According to an exemplary embodiment, the counterweight is arranged around the housing of the hammering element. In this way, the counterweight is completely distributed around the tool. By designing the counterweight as one unitary part, whereby the impact machine may be better balanced. Another advantage is that the frequency of a single unit is easier to control.
According to an exemplary embodiment, a boost of pressurized air is directed to the counterweight through the outlet hole from the impact element. The counterweight is designed in such a way that it directs the air in a direction that it creates a axial force on the counterweight, bringing it into counter phase of the hammering element in a short time and thereby reducing the vibrations. An advantage is that the vibration damping arrangement is rapidly brought into the correct working frequency and that the vibration reduction effect is achieved faster.
According to an exemplary embodiment, the vibration reduction arrangement may be enclosed in a housing. An enclosed vibration reduction arrangement may reduce the occurrence of foreign particles (dust, dirt etc.) enter the system.
According to an exemplary embodiment, the housing of the vibration reduction arrangement is a closed housing, which contains a fluid. The fluid can be air, gas a liquid. The fluid may be introduced to either reduce friction or to create a damping effect.
The force from the counterweight on the housing also creates a feed force that improves the efficiency of the machine.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the [element; device, component, means, step, etc]” are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise.
Other objectives, features and advantages of the present invention will appear from the following detailed disclosure, as well as from the drawings.